To make a press accessible for fitting and maintenance work and for repairs to the ram and ram drive, etc., it is necessary to bring the ram into a convenient working position and to secure it there. This can be done by means of ram locking devices according to German Offenlegungsschrift 3 316 364. The known ram locking device comprises a guide rod, mounted concentrically and rotatably in a housing, for a slidably movable spindle that is adjustable relative to the guide rod. The lower end of the spindle projects from the housing on the ram side and is secured to a tension rod carrying a locking member or a tension rod head that faces a corresponding receiving opening on the ram. A rotary movement given to the guide rod is transmitted to the spindle carrying the tension rod and leads to angular displacement of the spindle relative to the housing.
Since the ram of a large press can weigh up to 300 t, several such ram locking devices, preferably four in the case of heavy rams, are always fitted on the crown of the press frame. As soon as the spindle of a ram locking device is adjusted downwards, e.g. by means of an adjusting nut fitted around the externally threaded spindle, the head of the tension rod enters the receiving opening or recess of the ram. After the locking members of all the ram locking devices have been moved into engagement in the corresponding receiving openings of the ram, the locking members, which are shaped as hammer heads, are swivelled through 90.degree. into the retaining position by rotating the spindle. In the retaining position the ram locking device then moves upwards until the tension rod or its head meets the locking bracket of the ram. Since the operating force of each of the locking devices is the same, the load of the ram is distributed equally over all the retaining points.
This and other known ram locking devices suffer from the disadvantage that the great weight of the press ram resting or supported on the tension rod heads and the resulting high frictional forces make it extremely difficult to release the locking device. Hence locking systems that use threaded spindles, inclined planes, detent pawls or the like can no longer be automatically released under the weight of the ram. Before releasing the locking device the tension rods supporting the full weight of the ram must therefore first be relieved of their load. In the known locking devices this is done by raising the ram, for example by means of the main drive or via the ram adjusting means; in each case considerable additional effort is required.
It is therefore an object of the invention to facilitate unlocking, and in particular release of the tension rod, of a ram locking device of the above-mentioned kind, without having to raise the ram.